MATH 023

MATH 023 - 1-1 1 Experiment 1 - Electric Fields and...

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1-1 1 Experiment 1 - Electric Fields and Electric Potentials For reasons that will be discussed later in Physics 13 and 21, Coulomb's law for the forces between charges is often rewritten in terms of the force exerted on each charge by the electric field E created by all other charges; that is, 1 (on 1) = q FE ( with E due to all other charges); Eq. (1-1). If the locations and values of all other charges are known, we can calculate the electric field in Eq. (1). However, in many cases, the other charges are not known initially. Instead, electric potentials on the boundaries are specified, where the electric potential difference (in volts, V) between two points is given by the line integral Vd E ; Eq. (1-2), between these points. The minus sign in Eq. (1-2) means that the "voltage" decreases if the distance moved d is in the direction of the electric field. Since cos( ) d E d E , where is the angle between the directions of E and d , see Fig. 1, the magnitude of V is greatest if is zero or 180 o ; i.e., E and d are in the same or opposite directions. Fig. 1. V greatest if = 0 or 180 o NOTE : You will do this experiment alone! In future experiments, you will work with a partner. EXPERIMENT - PART 1: Equipotential Lines (surfaces in 3-D.) In order to “go green,” we are now using dry contacts between the electrodes and the black paper. It is better for the environment, but in order to make good contact between the metal and the black paper, you need to make sure to press down FIRMLY! 1) Fasten the sheet of black conductive paper to the cork board with four push pins at the corners. 2) Use the tip of a pencil to put a heavy layer of powdery graphite from the pencil lead on the raised edges on the bottom of both the metal disk and metal strip.
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MATH 023 - 1-1 1 Experiment 1 - Electric Fields and...

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